Multilayer Element and a Method for Producing a Multilayer Element

ABSTRACT

A ceramic multilayer element can be produced by pressing together a plurality of ceramic multilayer segments. Each multilayer segment includes a stack of a plurality of ceramic layers that are pressed together.

This application is a continuation of co-pending InternationalApplication No. PCT/EP2008/051220, filed Jan. 31, 2008, which designatedthe United States and was not published in English, and which claimspriority to German Application No. 10 2007 005 341.1 filed Feb. 2, 2007,both of which applications are incorporated herein by reference.

TECHNICAL FIELD

A method for producing a multilayer element is described, for example, amethod in which the multilayer segments are pressed together. Alsodescribed is a multilayer element with predetermined breakage regions.

BACKGROUND

A method for making a multilayer actuator is known from the Germanpublication DE 102 34 787 C1. Microdistortions are intentionally made inthe actuator framework, which grow inwardly upon polarization of theactuator.

An electrical multilayer element with ceramic layers arranged along alengthwise axis, where at least one predetermined breakage layer isarranged at a point on the lengthwise axis between ceramic layers isknown from International publication WO 2004/077583. It is less stableto tensile stresses in the lengthwise direction than are the ceramiclayers.

SUMMARY

In various aspects, the present invention provides an electricalmultilayer element that remains functional under repeated mechanicalstresses and a method for producing such a multilayer element.

For example, the invention specifies a method for producing a ceramicmultilayer element in which a number of ceramic multilayer segments arepressed together. The ceramic multilayer segments each have a pluralityof ceramic layers pressed together.

A multilayer segment is understood to mean a stack of at least twoceramic layers with any outer contour. A multilayer element results froma stack of multilayer segments arranged one on top of another andpressed together.

Thin multilayer segments are made available, the external shaping ofwhich can take place, for example, by means of a cutting tool, withoutdamaging the multilayer segments, and optionally using a lessenergetically or less powerfully driven cutting tool can be enabled bythe choice of a certain small number of pressed ceramic layers. Since aplurality of the multilayer segments formed in this way are pressedtogether, a complete multilayer element, for example, a piezoelectricmultilayer element, can be created with the desired outer contour andthickness. Here the outer contour is at least in part rounded, circularor oval.

Thus, there is a decisive advantage over multilayer elements that arefirst cut to size only after they have reached their ultimate thicknessand are subject to damage, since the cutting means used for this must bedriven with great force through a great deal of material in one pass.

Compared to multilayer elements in which individual, already cut tosize, ceramic layers are stacked one on top of another, there is theadvantage of eliminating the stacking of each separate, already cutceramic layer with another ceramic layer.

Also, handling of multilayer segments, for example, during transport, iseasier than with individual ceramic layers. The probability of processerrors, which can accumulate with each separation of a ceramic layer,can be minimized.

The production time for a multilayer element is advantageouslysignificantly reduced, since each individual ceramic layer does not haveto be placed on another ceramic layer.

The production process offers the advantage that multilayer elements canbe created in any height. This makes it possible to design elements thatsatisfy certain criteria that apply in the case of tight placementconditions when inserted into a device that uses the multilayer element.

Another advantage is that multilayer elements can already be created inan unsintered, i.e., green, state with a desired outer contour. Thiseliminates the need, for example, to give a sintered element the desiredexternal geometry by means of a cost- and time-intensive grindingoperation. Where this step is omitted, it is possible, for example, toapply external contacts flush or directly onto the sintered element.Thus, this produces an additional beneficial effect.

Preferably, a plurality of ceramic films are pressed together into afilm stack as a precursor product, where the ceramic films preferablycontain an organic binder, so that the pressing, or handling, of thefilms, for example, in transport, is made easier.

The ceramic film stack or the stacked ceramic films have a large surfacein relationship to the cross-sectional area of a ceramic multilayersegment that is to be separated out later, i.e., the ceramic film stack,as a precursor product, preferably comprises a multiple of the area ofthe multilayer segments to be separated out later, which are called theafterproduct.

It turns out to be particularly favorable if the temperature at whichthe ceramic films are pressed together is lower than the temperature atwhich the multilayer segments are pressed together. This will achievebonding of the multilayer segments to each other such that, at least inthe ultimately sintered element, the boundary region between themultilayer segments has lower resistance to tensile stresses. Incomparison, the ceramic layers of an individual multilayer segment arefirmly bonded together.

According to a preferred embodiment of the production process, thebinding effect of the organic binder while pressing the multilayersegments is set to be different than the binding effect during thepressing of the ceramic films. Preferably, here a binder is selectedwhose activity is dependent on a number of process parameters, forexample, temperature, force with which the multilayer segments arepressed together, duration of the pressing force, and the atmosphere orcomposition of the atmosphere in which the films and/or the multilayersegments are pressed together. Controlled change of the activity of thebinder has the advantage that the binding or adhesion of the multilayersegments to each other can be controlled.

According to one embodiment, the ceramic layers contained in themultilayer segments are in the green state during the pressingoperation. This means that the multilayer segments do not first have tobe separately sintered.

The temperature at which the ceramic films are pressed togetherpreferably varies from room temperature by a maximum of 25%. Thetemperature at which the multilayer segments are pressed togetherpreferably lies between 75° C. and 95° C.

It is preferred that the tensile strengths of the boundary regionbetween the multilayer segments be determined by adjusting thetemperature at which the multilayer segments are pressed together.

The tensile strength of the boundary region between the multilayersegments can also be determined by adjusting the pressure applied inpressing the multilayer segments.

In addition or alternatively, the tensile strength of the boundaryregion between the multilayer segments can be determined by adjustingthe duration of the pressing of the multilayer segments.

By adjusting the process parameters of temperature, pressure and/orduration of pressing, a tensile strength is determined for the boundaryregion between two multilayer segments that gives these segments thefunction of a predetermined breakage region. Thus, in each caseaccording to the use of the multilayer element, it is possible to designa predetermined breakage region that responds or forms a crack atcertain mechanical stresses. The predetermined breakage region thusforms a tailored mechanical weak point in the multilayer element.

A predetermined breakage region that arises between two multilayersegments of a multilayer element by means of a production processdescribed in this document allows, under certain tensile stresses, acontrolled cracking into the interior of the multilayer element. Thecracking thus runs essentially parallel to the plane of the ceramiclayers.

The multilayer segments are preferably cut from the precursor foil stackby means of a cutting tool. They can be cut out with any desired outercontour. Thus, multilayer segments are cut with, in particular, circularor oval contours or at least nearly circular or oval contours, so thatmultilayer elements with such contours can be created for high qualityor stability demands.

From the standpoint of process engineering, it turns out to beparticularly advantageous if the cutting tool directly transports theseparated multilayer segments further on, for example, to anothermanufacturing unit for further processing.

According to one embodiment, the multilayer segments are transportedinto a cavity for pressing. By means of such a method, the need for aconveyor means that is used only for transport, for example, a conveyorbelt or gripper, is omitted.

If a stamping tool is used as the cutting tool, the multilayer segmentscan be cut from the foil stack with particular speed. Since the foilstack is, relatively speaking, not very thick, the stamping tool canstamp out the likewise relatively thin multilayer segments with anycross-sectional shape without damaging them.

Preferably, in each case, two adjacent multilayer segments are pressedtogether in a repeated operation. For a multilayer element that has, forexample, 50 multilayer segments, then 49 pressing operations are carriedout, one for each pair of adjacent multilayer segments. The number ofpressing operations is thus one less than the number of multilayersegments in the end multilayer element.

According to one embodiment of the method, the multilayer segments arepressed together by pressing a stamping tool onto a face surface of amultilayer segment which has been inserted into the cavity. Themultilayer segment on which the stamping tool presses is always in theuppermost position in the cavity.

According to another embodiment of the manufacturing process, themultilayer segments are pressed together with the additional use of apress pin, which presses against the undermost multilayer segment in thecavity, toward the stamping tool.

Ceramic films with imprinted metallizations can be used to produce themultilayer segments. These metallizations can later serve as electrodesor electrode layers of the ultimately produced multilayer element.

Warpage during pressing which might lead to bending of internalelectrodes that may be present, at least at the ends of the multilayerelement, is highly minimized by means of the production process, sinceindividual multilayer segments are pressed together rather than anentire multilayer element of greater thickness. This minimizes convex orconcave bending of the internal electrodes (with respect to the axisrunning through the multilayer element in the vertical direction). Allin all, a multilayer element with high symmetry is created.

A piezoelectric multilayer element can be created by means of theproduction process. For this, the ceramic layers preferably contain aPZT (lead zirconate titanate) ceramic. These ceramic films can contain abinder, which is burned out during a debinding before the multilayerelement is subjected to a sintering operation.

In addition, a multilayer element with a stack of ceramic layers andelectrode layers arranged on top of one another is specified, where apredetermined breakage region with reduced tensile strength runningparallel to the ceramic layers is localized between adjacent ceramiclayers and partially merges into them. Adjacent ceramic layers thus havea portion of the predetermined breakage region.

The multilayer element has a plurality of multilayer segments that arepressed together and that have individual ceramic layers, and thesesegments are sintered together. With that, the predetermined breakageregion runs between adjacent ceramic layers and partially penetratesinto them or is partially contained in the ceramic layers. Adjacentceramic layers belonging to different multilayer segments form parts ofthe predetermined breakage region.

The multilayer element or the multilayer segments which it comprises arepreferably a product of the production process described in thisdocument in all of its possible embodiments.

The predetermined breakage region according to one embodiment has aporosity that is higher than the average porosity of the ceramic layersin the overall multilayer element.

Edge- or face-side ceramic layers of adjacent multilayer segments canhave regions that abut one another or merge into one another and thathave less tensile strength or are more porous than the ceramic layersthat are turned away from the boundary between the multilayer segments.The elevated porosity can also be understood as lower packing density ofthe ceramic grains in the corresponding region.

The predetermined breakage region between the multilayer segments formsa crack running into the interior of the multilayer element when themultilayer element is subjected to certain mechanical stresses. If anelectrode layer or a flat metallization is arranged between themultilayer segments, the crack will run along or parallel to theelectrode or through the electrode layer, and thus does not connect twoelectrodes that are arranged one above the other. An electric shortcircuit that would lead to failure of the multilayer element can thus beavoided.

The multilayer element preferably has a plurality of predeterminedbreakage regions distributed over the thickness of the multilayerelement at regular intervals. The intervals, i.e., the space between twoadjacent predetermined breakage regions, comprise a plurality of ceramiclayers and electrode layers, between which no predetermined breakageregion is made available.

BRIEF DESCRIPTION OF THE DRAWINGS

The described embodiments are described in more detail by means of thefollowing embodiment examples. Here:

FIG. 1, which includes FIGS. 1 a and 1 b, shows a multilayer elementwith a predetermined breakage site in a first arrangement;

FIG. 2, which includes FIGS. 2 a and 2 b, shows a multilayer elementwith a predetermined breakage site in a second arrangement;

FIG. 3 shows a cross-sectional view of a multilayer element;

FIG. 4 shows a perspective view of a part of an essentially massiveblock comprising a cavity, with a partially inserted punching tool;

FIG. 5 shows a top view of an essentially massive block comprising acavity; and

FIG. 6 shows a side view of an essentially massive block comprising acavity, with a partially inserted punching tool.

The following list of reference symbols may be used in conjunction withthe drawings:

-   -   1 Multilayer element    -   2 Ceramic layer    -   3 Electrode layer    -   4 Multilayer segment    -   5 Predetermined breakage site    -   6 External contact    -   7 Massive block    -   8 Cavity    -   9 Punch tool    -   10 Bottom-side opening of cavity    -   11 Vertical fastener drilling    -   12 Horizontal drilling    -   13 Upper side opening of cavity    -   A-A Section line

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 a shows a multilayer element 1 with ceramic layers 2 andelectrode layers 3 arranged alternately one above the other. FIG. 1 bshows a magnified section from FIG. 1 a. The multilayer element has aplurality of multilayer segments 4, each of which has a plurality ofceramic layers and electrode layers. Between each two adjacentmultilayer segments 4 is a predetermined breakage region 5, which isdesigned as a region with reduced strength compared to the surface areasbetween other ceramic layers deeper into the interior of each multilayersegment 4. The predetermined breakage region 5 is contained in theboundary region between two adjacent multilayer segments and merges withits reduced mechanical strength into an undermost and uppermost ceramiclayer of adjacent multilayer segments.

The predetermined breakage region 5 is realized, by means of the methodof producing the multilayer element, as a region of reduced porosity bycomparison with the porosity of other ceramic layers within eachmultilayer segment 4. The elevated porosity in the boundary regionbetween two multilayer segments 4 can be determined by adjusting thecombination of the following parameters:

-   -   Temperature and/or applied pressure and duration of pressing        force at which the ceramic films are pressed together to form        the precursor product film stack,    -   Choice of a binder used for the ceramic films, its binding        effect in dependence on the parameters mentioned above,    -   Temperature and/or pressure and duration of pressure at which        the multilayer segments are pressed together.

FIG. 1 shows in particular how the boundary region between twomultilayer segments 4 can be designed. The boundary region with reducedtensile strength runs, according to one embodiment, between two edge- orface-side ceramic layers 2 of adjacent multilayer segments 4, where oneof the ceramic layers is provided with an imprinted internal electrodelayer 3. This means that the predetermined breakage site 5 runs throughthe internal electrode layer 2, or cracking caused by certain tensilestresses runs through the internal electrode layer.

FIG. 2 a shows a multilayer element 1 with ceramic layers 2 andelectrode layers 3 arranged alternately one above the other. FIG. 2 bshows an enlarged section from FIG. 1 a. In composition, this embodimentof the multilayer element corresponds to that of FIG. 1. Thepredetermined breakage region 5 on two adjacent multilayer segments,however, is designed differently here. It merges into two edge- orface-side and adjacent ceramic layers 2 of adjacent multilayer segments4, and there is no electrode layer 3 between these ceramic layers 2. Aconstruction of this kind can be achieved, for example, by stacking themultilayer segments stamped out of a film stack with differentorientations for pressing. This means that, for example, two multilayersegments 4 that are adjacent and pressed together can have face surfacesturned toward each other, with these face surfaces free of internalelectrode layers 3.

FIG. 3 shows a multilayer element 1 with a preferred contour in a topview. The multilayer element or each multilayer segment 4 of themultilayer element in this case is circular in cross section, with flatsides. In a particularly favorable way, external electrodes 6 can beapplied to or arranged on the flattened side, where the electrodes areeach in contact with a set of internal electrode layers 3 arranged oneabove the other and having the same electric polarity.

The multilayer element or its multilayer segments preferably have adiameter of 8-10 mm; the flattened sides each have a length of 2-4 mm.

Preferably, the following operation is chosen to produce the multilayerelement.

According to one embodiment, in producing a multilayer element, afterthe addition of a suitable binder and disperser system in the form of aslurry, a ceramic powder with piezoelectric properties is processed intofilms.

The films are imprinted according to the desired design with anelectrode paste, in particular, screen-printed, so that an isolationzone on the flattened segments of the multilayer element is madeavailable. The isolation zone comprises a nearly field-free region,where adjacent internal electrodes do not overlap. Each film is againimprinted, where the printing of adjacent films of a film stack takesplace with an offset.

This is followed by the lamination or stacking of, preferably, 25-50films. They are pressed together to a thickness of 1-2 mm by means of apressing operation at about room temperature under a weight of 100metric tons, with respect to an area of 105×105 mm². The dielectricthickness of each ceramic film is then about 100-120 μm. The lowthickness of the film stack enables multilayer segments of any kind tobe cut from the film stack, preferably ones with a round, oval oroctagonal cross section.

Multilayer segments with the desired cross-sectional shape are stampedout of the pressed film stack with a stamp. The stamp or stamping toolcomprises a sharp projecting edge for stamping out multilayer sequences;further inward, it has a flat area that presses on the multilayersegment surface and separates it from the film stack.

Advantageously, the stamped-out multilayer segments, in contrast toindividual ceramic layers (which each come from a single ceramic film)are much easier to handle in the process of manufacturing the multilayerelement. For example, they can be grabbed and transported better. Inthis case, the risk of damage to these multilayer segments is alsoreduced. The effectiveness of these advantages is especially apparentwhen the cross-sectional area of the stamped out multilayer segment is20 mm² or smaller.

The multilayer segments with low height that are stamped from the filmstack or stacks are preferably stacked in a cavity by means of thestamping tool. A multilayer segment is pressed onto a multilayer segmentor partial multilayer element that is already in the cavity, at a forceof 1500 N at about 85° C. The operation is repeated until apiezoelectric multilayer element with any desired height, preferablybetween 70 and 100 mm, is made.

The advantage of pressing small volumes becomes clear in this case,since the scatter of the applied pressure is relatively small withrespect to a small area. Frictional forces on the inner walls of thecavity that arise are smaller than in the case of larger multilayerelements, for example, ones that have a height of 10-1000 mm. Thus,multilayer elements with extremely high symmetry can be made; pressingwarpages can no longer be detected in a completed multilayer element.Moreover, the production process provides that internal electrodes thatmay be present in a multilayer element are not affected or are onlyminimally affected by warpage or bending. In the absence of the pressingwarpage noted above, internal electrode parts that are creased or bentover at the edge of the multilayer element are no longer seen.

Preferably used criteria for establishing the absolute breaking force atthe seam between the multilayer segments are the applied pressure,temperature or hold time in a pressing operation.

A still-green multilayer element produced by pressing multilayersegments can then be debinded and sintered. External contacts can thenbe applied to the side surfaces of the multilayer element.

Measurement of multilayer elements made by pressing multilayer segmentsshow a seam region between two adjacent multilayer segments with lowerstrength than the bonds between individual ceramic layers lying in themultilayer segments. An advantage of this effect was seen to be that themultilayer element, because of the weaker seam regions, contains one ormore predetermined breakage sites that favor a stable failure orcontrolled failure of the multilayer element. Additional process ormanufacturing steps to introduce predetermined breakage sites into theelement can thus be omitted. From the standpoint of manufacturingtechnology, the number of predetermined breakage sites alone is alreadydetermined by the height of the multilayer element, since a certainheight of the multilayer element implies a number of multilayer segmentboundaries and thus predetermined breakage regions.

The predetermined breakage region responds at certain tensile stresses,where it forms a crack running parallel to the ceramic layers orelectrode layers. Since the dielectric cannot be entirely broken throughin the direction between two internal electrodes by the crack, a shortcircuit between two electric poles of the multilayer element supportedby internal electrodes situated one above the other caused by certaintensile stresses can be avoided.

FIGS. 4-6 show different perspective views of a preferably massivemetallic block 7, in which multilayer segments are pressed together toform a multilayer element 1 in a cavity 8 by means of a stamping tool 9.

For illustration, FIG. 4 shows a section of a preferably massive andmetallic block 7 in a perspective view.

The block has the following dimensions: width=130-170 mm, height=115-155mm, depth=30-70 mm. A cavity 8, which is realized as a drilling, runscentrally and vertically through block 7. The cavity 8 has an opening 10at the bottom that allows the insertion of a press pin, not shown, whichpushes against a stamping tool 9, which is shown inserted into thecavity. The cavity 8 has an internal clear diameter that is dimensionedso that a multilayer segment can be inserted into the cavity 8 togetherwith the transport means or stamping tool 9 that surrounds andtransports the multilayer segment.

Multilayer segments arranged between the press pin, which pushes frombelow, and the stamping tool 9, inserted from above, are pressedtogether.

According to one embodiment, the press block 7 has a number of partsthat are positioned on locating pin(s) and secured with screws. However,the press block can also be made in one piece, i.e., from a casting.

Preferably, the press block is made of steel, and other materials suchas ceramic, sintered materials or other hard metals can be used.

The press block 7 has a plurality of vertically running drillings 11,which according to one embodiment serve to secure the block 7 by meansof screws or other fastening means to another object, for example,another housing. Horizontal fastener drillings 12 are also shown. Bymeans of suitable fasteners such as screws, the horizontal fastenerdrillings 12 serve for assembly of the possibly several parts of theblock 7 (of which only one part is shown by this figure) into a blockunit.

According to an advantageous embodiment, heating elements are insertedinto the vertically running drillings 11 to heat the press block. Theheating elements can be realized as heating resistance wires. Theheating elements can be contained in drillings 11 together with afastening element if the drillings 11 are also used to fasten the pressblock.

FIG. 5 shows a top view of block 7 that is shown only partially inperspective view in FIG. 4. An opening of cavity 8 is shown on the topside and centrally arranged in the block. The section line A-A is alsoshown; a section of the entire block through this section line was shownin the previous figure. The lateral course of the horizontal fastenerdrillings 12 and the openings of the vertical drillings 11 are shown.

FIG. 6 is a side view of block 7. The partially inserted stamping tool 9is shown at the top. The lateral course of a fastener drilling 12 isshown at the bottom.

1. A method for producing a ceramic multilayer element by pressingtogether a plurality of ceramic multilayer segments, each multilayersegment having a stack of a plurality of ceramic layers that are pressedtogether.
 2. The method as claimed in claim 1, further comprisingproducing the multilayer segment by pressing together a plurality ofceramic films into a film stack, each ceramic film containing an organicbinder.
 3. The method as claimed in claim 2, wherein a temperature atwhich the ceramic films are pressed together is lower than a temperatureat which the multilayer segments are pressed together.
 4. The method asclaimed in claim 2, wherein a binding effect of the organic binderduring the pressing of the multilayer segments differs from a bindingeffect during the pressing of the ceramic films.
 5. The method asclaimed in claim 1, wherein during the pressing of the multilayersegments, the ceramic layers contained therein are in a green state. 6.The method as claimed in claim 3, wherein the temperature at which theceramic films are pressed together deviates by a maximum of 25% fromroom temperature, and the temperature at which the multilayer segmentsare pressed together is between 75° C. and 95° C.
 7. The method asclaimed in claim 1, wherein the multilayer element includes a boundaryregion between the multilayer segments in an end multilayer element thatprovides the ceramic multilayer element with a function, the boundaryregion having a tensile strength such that causes the boundary region tofunction as a predetermined breakage region, the tensile strength beingdetermined by adjusting the temperature at which the multilayer segmentsare pressed together.
 8. The method as claimed in claim 1, wherein themultilayer element includes a boundary region between the multilayersegments in an end multilayer element that provides the ceramicmultilayer element with a function, the boundary region having a tensilestrength that causes the boundary region to function as a predeterminedbreakage region, the tensile strength being determined by adjusting apressing force applied during the pressing of the multilayer segments.9. The method as claimed in claim 1, wherein of the multilayer elementincludes a boundary region between the multilayer segments in an endmultilayer element that provides the ceramic multilayer element with afunction, the boundary region having a tensile strength that causes theboundary region to function as a predetermined breakage region, is thetensile strength being determined by adjusting a duration of thepressing of the multilayer segments.
 10. The method as claimed in claim2, further comprising separating the multilayer segments from the filmstack using a cutting tool.
 11. The method as claimed in claim 10,wherein the multilayer segments are separated from the film stack with acontour shape.
 12. The method as claimed in claim 11, wherein themultilayer segments have one of the following contour shapes: rounded,circular with flattened sides, circular, or oval.
 13. The method asclaimed in claim 10, wherein the cutting tool transports the separatedmultilayer segments.
 14. The method as claimed in claim 13, wherein thecutting tool transports the separated multilayer segments into a cavityfor pressing.
 15. The method as claimed in claim 10, wherein the cuttingtool comprises a stamping tool.
 16. The method as claimed in claim 15,wherein the multilayer segments are pressed together by the stampingtool pressing on a face surface of the multilayer segment that was lastinserted into the cavity.
 17. The method as claimed in claim 16, whereinthe multilayer segments are pressed together with the additional use ofa press pin that presses on an undermost multilayer segment that is inthe cavity, toward the stamping tool.
 18. The method as claimed in claim1, wherein the multilayer segments are pressed together with a height of0.8 mm to 1.2 mm.
 19. The method as claimed in claim 1, wherein themultilayer segments are pressed to produce the ceramic multilayerelement with a height of 70 mm to 100 mm.
 20. The method as claimed inclaim 1, wherein the multilayer segments are pressed together with across-sectional area of less than 110 mm².
 21. The method as claimed inclaim 1, wherein the multilayer element is debinded.
 22. The method asclaimed in claim 1, wherein the multilayer element is sintered.
 23. Themethod as claimed in claim 2, wherein the ceramic films comprise ceramicfilms with imprinted metallizations.
 24. The method as claimed in claim1, wherein the multilayer element forms at least a part of apiezoelectric multilayer element.
 25. A multilayer element comprising: astack of ceramic layers and electrode layers arranged one on top ofanother, wherein a predetermined breakage region runs parallel to theceramic layers and has reduced tensile strength, the breakage regionbeing localized between adjacent ceramic layers and in parts of theceramic layers.
 26. The multilayer element as claimed in claim 25,wherein an electrode layer is arranged between the adjacent ceramiclayers, and wherein the predetermined breakage region is partiallycontained in the electrode layer.
 27. The multilayer element as claimedin claim 25, wherein the predetermined breakage region is one of aplurality of predetermined breakage regions that are distributed over aheight of the multilayer element at regular distances, the distanceseach comprising a plurality of ceramic layers and electrode layers. 28.The multilayer element as claimed in claim 25, wherein the multilayerelement has a plurality of multilayer segments stacked one on top ofanother, each of the multilayer segments having a plurality of ceramiclayers and electrode layers, wherein the predetermined breakage regionruns between adjacent multilayer segments and is partially contained inthem.
 29. The multilayer element as claimed in claim 25, wherein thepredetermined breakage region has a porosity that is higher than anaverage porosity of the ceramic layers in the multilayer element.